Devices which use various types of recording disks, such as optical disks, magneto-optical disks, or flexible magnetic-recording disks, are known as disk drive devices. Of these, the HDD has spread widely as a storage device for computers and is becoming an indispensable information-storage device in current computer systems. In addition, HDD applications, such as video recording and playback devices, car navigation systems, or portable telephones, are increasing because of the superior characteristics of HDDs.
A magnetic-recording disk used in an HDD has a plurality of data tracks and a plurality of servo tracks formed in concentric circles on the magnetic-recording disk. A plurality of data sectors containing user data is recorded in each data track. Each servo track contains address information. The servo tracks are constructed from a plurality of servo data regions separated in the circumferential direction; and, one or a plurality of data sectors is recorded between the servo data regions. By accessing the desired data sector in accordance with the address information of the servo data, a magnetic-recording head can write data to a data sector and read back data from a data sector.
Typically, the HDD includes an integrated circuit (IC), which includes an amplification circuit for amplifying the signal of the head-slider disposed inside of the disk enclosure (DE). Normally, the IC is secured in a module in the vicinity of the pivot shaft of the actuator. Therefore, as described herein, this IC is referred to as arm electronics (AE), which is included in an arm-electronics (AE) module. The amplification circuit in the AE module amplifies the user data signal and the servo data signal read back by the head-slider, as well as the user data signal written by a magnetic-recording head. The AE module includes an internal logic circuit for advanced functions in addition to the amplification circuit. The AE module operates in response to commands from the controller of the HDD. Generally, the IC including the controller, which is also an encapsulated IC, is mounted on a control circuit printed-circuit board (PCB) secured to the outside of the DE of the HDD. The AE module also includes a register. The controller controls the AE module by storing control data in the register. For example, the AE module selects the magnetic-recording head of a designated head-slider, and converts, for example, the write current value, or alternatively, the sense current value, in response to commands from the controller. In addition, a power supply to a heater that is disposed on the head-slider is another function provided in circuits of the AE module.
The clearance between the magnetic-recording head flying in proximity with a recording surface of the magnetic-recording disk and the magnetic-recording disk, referred to herein as the “fly-height,” may be reduced in order to increase the areal recording density (AD) on the magnetic-recording disk of the HDD. Therefore, a technique for adjusting the fly-height has been used in the art of magnetic-recording in HDDs. In this technique, a heater is disposed on the head-slider; and, the fly-height is adjusted by heating the magnetic-recording head with the heater. As described herein, this technique is referred to as thermal fly-height control (TFC). TFC supplies current to the heater to generate heat; and, the magnetic-recording head protrudes outwards by thermal expansion. Thus, the fly-height between the magnetic-recording disk and the magnetic-recording head may be reduced.
To increase AD, the fly-height between the magnetic-recording head of the head-slider and the magnetic-recording disk is made as small as possible. The current fly-height is approximately several nanometers (nm). When the design margins in the structure of the HDD are considered, the fly-height is at a value close to the limit. Therefore, engineers and scientists engaged in HDD manufacturing and development are interested in finding ways to increase AD by more accurately controlling the fly-height.